The bonobo (Pan paniscus) is a great ape most closely related to the chimpanzee. It lives in a remote rain-forest region of central Africa, and was only identified as a species in 1933. Often referred to as the pygmy chimpanzee the body weight of the bonobo is, on average, the same or slightly less than that of the eastern common chimpanzee. The center of gravity is lower, making it possible for the bonobo to stand more erect and walk on two feet. Bonobos have longer limbs and their build is generally more slender and graceful than chimpanzees. The head and ears of bonobos are noticeably smaller, and there is less brow mass over the eyes. The facial skin is darkly pigmented, and the hair is black, usually parted in the middle of the head with bushy sideburns on both sides of the face. The bonobo’s vocalizations are high-pitched squeals.